Long term evolution (LTE) of third generation partnership project (3GPP) is being pursued to develop evolved universal terrestrial radio access (E-UTRA) and evolved universal terrestrial radio access network (E-UTRAN). The objects of the E-UTRA and E-UTRAN are to develop a radio access network supporting a high data rate, low latency, packet optimized system with improved system capacity and coverage. For example, in LTE, instead of current 3GPP code division multiple access (CDMA) technologies, orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) air interface technologies will be used in the downlink and uplink, respectively.
In order to support mobility in the E-UTRAN, a user equipment (UE) needs to perform handover related measurements on neighbor cells. The neighbor cell measurements shall be performed in a wide range of realistic and typical deployment scenarios, which include cells on the serving frequency, cells belonging to another frequency, or cells employing other access technologies, such as universal terrestrial radio access network (UTRAN) and global system for mobile communications (GSM)/enhanced data rates for GSM evolution (EDGE) radio access network (GERAN) systems.
A UE reports measurements to the network upon occurrence of a certain event or periodically. In certain situations it is sufficient that the UE starts the periodic reporting after the occurrence of an event. According to this hybrid reporting mechanism when a particular measurement exceeds a pre-specified threshold, the UE switches to periodic reporting after reporting the event, (i.e., event triggered periodical reporting).
The main advantage of the event triggered periodical reporting is that the network does not have to configure periodic reporting for an infinite period of time. This has an advantage of considerably reducing signalling overheads since periodic reporting would commence only when desired. Another advantage is that unlike periodic reporting the UE does not have to report measurements when they are not needed from network perspective.
One typical situation that the event triggered periodic reporting is desired is characterized by a corner effect where there is an abrupt change in path loss. In the wake of such unexpected event, it is desirable for the network to receive periodic reports. These situations are quite typical at some locations in dense urban environment.
Within the measurement reporting criteria field in the measurement control message, the UTRAN notifies the UE which events should trigger a measurement report. The listed events are the toolbox from which the UTRAN can choose the reporting events that are needed for the implemented handover evaluation function or other radio network functions. All the specified events are measured with respect to any of the measurement quantities.
The conventional reporting mechanism has some problems to be implemented in the LTE network. First, currently, there is no definition of events for LTE which reflects the LTE specific characteristics. The events defined for universal mobile telecommunications system (UMTS) reflect the channel and frame structure of CDMA system and they cannot be applied to the LTE system which has an OFDM-based frame structure. For example, the primary common pilot channel (CPICH) used in UMTS for event definition is no longer applicable for the LTE system since the CPICH is not existing at all. So events reflecting the LTE system characteristics should be provided
Second, there is no mechanism available in the LTE system for event triggered periodic measurement reporting. The mechanism used in UMTS cannot be directly used in LTE for event triggered periodic reporting because in order to better utilize the system resources, no dedicated channel is allocated to the UE in LTE and an active set is no longer maintained for the LTE operations including measurement and measurement reporting. Therefore, a modified mechanism should be provided for LTE.
Third, in the LTE system, there is no dedicated uplink channel. Therefore, a mechanism for request and scheduling of uplink resource for periodic measurement reporting after certain event is necessary.